On 24 May 2013 18:00, Dave <e...@dc9.tzo.com> wrote: > I think index homing on a gantry would only be worthwhile if home > offsets could be applied after the index/marker pulse was found.
They are. When the index is seen then the axis position is set to the HOME_OFFSET from the INI file. (Actually, I am making an assumption there, it is set on the basis of joint->home_offset, which I am assuming is read in from the INI file). So, the sequence, for index-homing, as it stands is: 1) Both motors move towards home at the same speed. 2) One motor finds a limit switch, waits 0.1 seconds, then reverses direction and moves at the latch velocity. 3) The other motor finds the limit switch, waits 0.1 seconds, then reverses direction and moves at latch velocity. 4) One motor (could be either) sees the index, and the axis position is set to HOME_OFFSET. It then rapids to HOME_POSITION 5) The other motor sees its index, and sets its position to it's HOME_OFFSET. And does a rapid to HOME_POSITION. During 1) the gantry twist should not change. During 2) the twist should initially decrease as the sides converge (assuming that the limit switches are good enough). But once they have crossed, it is getting worse. During 3) the motors are turning at the same rate, so twist does at last not get any worse, at least until the rapid-to-home. During 4) the rapid is a serious concern. During 5) the motors will be chasing each other, to a final perfectly-squared state. Incidentally, I doubt that this gantry is as rigid as it is being made out to be. If it was that rigid then it wouldn't need two motors :-) I think that as long as the HOME_POSITION is as close as possible to zero (minimum movement in the rapid-to-home move) it is plausible to make up for encoder misalignment with differing HOME_OFFSETs. However this may not be possible with shared home/limit switches as the final move needs to be off of the switches. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
